Air pollution has become an acute problem in recent years, especially in areas of high density population wherein large amounts of rubbish and waste material must be disposed of by incineration. Since much of the rubbish and waste material is not biodegradable and, thus, cannot be buried where it would create other environmental problems in landfills and pollution of rivers, lakes, and other bodies of water, technology of incinerators has been increased with results that many incinerators made today reduce heavy smoke and other obnoxious waste discharged into the atmosphere, but these prior arrangements, while proving satisfactory to a certain extent, do not necessarily eliminate all of the harmful residues in the exhaust gases within standards set up by municipalities and/or the federal government. In those prior art incinerators which do meet such standards, they have been found to be costly to manufacture and also costly to operate.
Basically, the prior art incinerators and other primary combustion apparatus, such as furnaces, gas heaters, or the like, have utilized the concept of secondary burning in efforts to reduce the residual waste in the exhaust gases and this has been done by providing secondary spaced burning zone or zones in the exhaust stack of the incinerator. These prior art arrangements do provide for the supply of air into the secondary burning zone or combustion chamber so as to supply additional oxygen to support combustion, but such air was drawn from atmosphere and discharged into the secondary combustion chamber as subsequently "cool" air. This necessitated burners utilizing more fuel to maintain the heat in the secondary combustion zone or chamber at a temperature necessary for the combustion of waste products. In many instances, this heat in the combustion chamber of the afterburner could not be maintained at a sufficient temperature to cause complete combustion throughout the complete operation cycle of the equipment and in other instances, it could not be raised sufficiently high to burn certain waste products in the exhaust gases. U.S. Pat. No. 3,403,645, issued Oct. 1, 1968 to George H. Flowers, Jr., and U.S. Pat. No. 3,489,109, issued Jan. 13, 1970 to George H. Flowers, Jr., and both assigned to the same Assignee as this application, disclose incinerators which utilize a two-stage combustion process for producing clean flue gases. In the first stage, burning of the bulk of the waste material is accomplished in a primary or main combustion chamber and the hot exhaust gases are discharged from this chamber into a second combustion chamber wherein additional air is supplied direct from atmosphere to further support the burning of any combustible products left in the exhaust gases. While the arrangements disclosed in these two patents do result in satisfactory elimination of air pollution for many waste materials, the temperatures within the secondary combustion chamber could not be raised high enough to support combustion of certain waste products without constantly utilizing the burner therein and this resulted in an expensive operation and the lack of conservation of fuel.
U.S. Pat. 3,408,167, issued Oct. 29, 1968 to Roy W. Burden, Jr., discloses an exhaust gas afterburner essentially for use with incinerators or other primary combustion devices, the afterburner being positioned in the stack or in a bypass portion of the stack. In the arrangement of the aforementioned patent, a burner is provided in an area where combustion is to take place and upstream of the burner and the burning zone or combustion chamber there is provided means for introducing air into the exhaust gases in a turbulent manner. While this arrangement is somewhat analogous to the aforementioned Flowers patents, it again utilizes atmospheric air for assisting in combustion and this air is substantially cool air which has not been purposely heated. Another difficulty in this particular arrangement is that air is introduced upstream of the burner area and, consequently, the air has a tendency to cool the exhaust gases, thus, necessitating a requirement for use of even more fuel in the burner to elevate the temperature in the combustion chamber to a temperature sufficient to burn the waste products from the exhaust gases. U.S. Pat. No. 3,511,224, issued May 12, 1970 to Samuel R. Powancher, discloses a smokehouse exhaust incinerator wherein exhaust gases from a smokehouse are mixed with fresh air and are discharged together into a combustion chamber having a burner. The incinerator of this latter-mentioned patent is somewhat similar to that of the Burden patent in that, again, there is a cooling of the exhaust gases prior to entry into the combustion chamber by mixture with air with this resulting in the disadvantages mentioned heretofore. Of course, in this arrangement, the purpose is to burn the exhaust gases to remove the smoke therefrom and, consequently, the temperatures necessary for this type of operation are not nearly as high as those temperatures required for burning waste products in exhaust gases where such waste products come from either solid or liquid waste or rubbish and wherein such waste material being burned is not biodegradable.